The present invention relates to brake boosters for motor vehicles and deals more specifically with a diaphragm support for such brake boosters.
Braking systems generally include a master cylinder intended to apply the pressure of the brake fluid to the brakes of a vehicle when a brake pedal is actuated.
Inserted between the master cylinder and the brake pedal is a brake booster, for example of the vacuum type.
There are various types of brake booster.
For example, a booster of this kind comprises, in the known way, an enclosure, a diaphragm mounted on a support and dividing the enclosure into a front chamber which is equipped with means for connection to a source of vacuum and a rear chamber, a piston which can move axially in the enclosure and on which the support is mounted, a plunger mounted so that it can be moved axially in the piston under the control of a brake pedal between an unstable forward braking position and a retreated stable position of rest, and a valve interacting with seats provided on the piston and on the plunger so as, on the one hand, to isolate the rear chamber from the ambient surroundings and to place this chamber in communication with the front chamber when the plunger is in the position of rest and, on the other hand, isolate the rear chamber from the front chamber and place the rear chamber in communication with the ambient surroundings during braking.
A booster of this kind allows the braking force applied to the brake pedal to be increased by a multiplying coefficient which may, for example, be as high as 9.
The forces which the diaphragm and its support have to withstand are relatively high. In particular, the radially internal region of the support, which is fixed to the piston, is very highly stressed in so far as the opposite peripheral region is free to oscillate.
In consequence, this region is subjected to bending forces that steel, which is often used for producing the supports, is incapable of withstanding in a durable manner, unless great thicknesses are used.
The object of the invention is to remedy this drawback.
The subject of the invention is therefore a diaphragm support for a motor vehicle brake booster, comprising a central region intended to be fixed to a piston of the brake booster and comprising a peripheral region, characterized in that at least part of the support extending from the central region towards the peripheral region includes a stratified structure consisting of a superposition of at least two sheets joined together.
The bending strength of the support is thus increased without the need to increase the thickness of the support.
This diaphragm support may also have one or more of the following features, taken in isolation or in any technically feasible combination:
the sheets are made of steel,
the sheets are made of aluminum,
an assembling material including an element chosen from polypropylene and polyamide is placed between the sheets,
the entire support is made of the said stratified structure,
the peripheral region has a folded-over or curved edge,
the said sheets have complementing local deformations formed near their peripheral region,
it includes additional means of joining the said sheets together, these means comprising at least one element chosen from screws, rivets, welding and bolts, provided near the peripheral region.
Another subject of the invention is a method for manufacturing a diaphragm support for a motor vehicle brake booster, characterized in that it consists in pressing a stratified panel consisting of an assembly of stacked sheets between which a material for joining the said sheets together is placed.
Finally, a further subject of the invention is a brake booster of the aforementioned type, characterized in that the support consists of a diaphragm support as defined hereinabove.